This easy kung pao beef features tender steak strips, colorful bell peppers, and crunchy peanuts in a perfectly balanced sweet and spicy sauce that's better than takeout.
Start by slicing your flank steak into thin strips, cutting against the grain for maximum tenderness.
1.75 pounds flank steak
In a small bowl, whisk together soy sauce and cornstarch until completely dissolved. Add brown sugar, rice vinegar, and sesame oil, whisking until well combined. Reserve 2 tablespoons for marinating the beef and set the rest aside for the final sauce.
¼ cup soy sauce, 3 teaspoons cornstarch, 3 tablespoons brown sugar, 2 tablespoon rice vinegar, 1 tablespoon sesame oil
Marinate the beef strips with the reserved 2 tablespoons of sauce for 15 minutes at room temperature. Meanwhile, add water to the remaining sauce ingredients and stir until smooth.
⅓ cup water
Heat your large skillet or large wok over medium-high heat with a tablespoon of oil. Sauté the bell peppers and onions for 3-5 minutes until they begin to soften, then add garlic and ginger for 1-2 minutes until fragrant. Transfer to a large bowl.
1-2 tablespoons vegetable oil, 1 red bell pepper, 1 green bell pepper, ½ medium onion, 3-4 cloves garlic, 2 teaspoons ginger
In the same pan over medium-high heat, sear the marinated beef strips until golden brown, about 2-3 minutes per side. Work in batches to avoid overcrowding, which would steam rather than sear the meat.
Add peanuts and dried red chilies to the skillet, stirring constantly for 30 seconds to 1 minute until fragrant. Return the beef and vegetables to the pan, pour the sauce over everything, and add red pepper flakes to taste. Reduce heat to medium and let everything simmer until the sauce thickens, about 3-4 minutes. The sauce should coat everything beautifully without being too thick.
¾ cup dry roasted peanut halves, 5 dried red chili peppers, 1 teaspoon red pepper flakes, Sliced green onions
Notes
Cut Against the Grain - Always slice your beef against the grain for the most tender results in stir-fries
High Heat is Key - Keep your heat at medium-high to achieve that perfect sear and prevent the vegetables from becoming mushy
Don't Overcrowd - Cook in batches if necessary to ensure everything gets properly seared rather than steamed
Taste and Adjust - Start with less heat and add more red pepper flakes at the end if needed - you can always add more spice
Prep Everything First - Have all ingredients ready before you start cooking, as this dish comes together very quickly